Apparatus and process for operating jet pump from which a driving medium exits at supersonic speed

ABSTRACT

A process for operating a jet pump with a driving nozzle from which a driving medium, especially steam, exits at supersonic speed, this driving medium mixing with a gaseous load medium. According to the invention, downstream of the outlet of the nozzle in the mixing region the circumferential length is increased by a cross-sectional shape of the driving jet diverging from the circle in order to eliminate the azimuthal symmetry of the vortex structure of the driving medium, wherein the respective cross-sectional surface corresponding to the principle of continuity beginning in the jet direction with a circular cross section in the supersonic portion of the jet corresponds to the circular cross-section surface of the driving medium in conventional supersonic nozzles. The invention is further directed to a jet pump, especially a steam jet pump, with a jet nozzle which widens from the neck to its end and is enclosed by a coaxially arranged mixing chamber and, a conically tapering diffuser portion adjoining the latter. This jet pump is characterized in that the cross-sectional shape of the widening portion (13) of the jet nozzle (10) is so formed by a neck (12) of the transonic portion having a circular cross section (Ak) with corresponding circumferential length (Lk) downstream of the jet that the circumference has a greater length (Lx) compared with the circular shape in a given cross-sectional surface (A), and at least three carrugations or beads (18) extending in the jet direction are provided in the casing (19) of the jet nozzle.

FIELD OF THE INVENTION

The invention is directed to a jet pump and process for operating thejet pump with a driving nozzle from which a driving medium, especiallysteam, exits at supersonic speed and is mixed with a gaseous loadmedium.

BACKGROUND OF THE INVENTION

In jet pumps in which a high-speed jet of driving fluid exerts a suctioneffect on a driven or pumped fluid and, in so doing, entrains thisfluid, the driving fluid imparts kinetic energy to the driven fluid bymixing of streams and by transfer of momentum so that a mixed jet ofboth fluids has a lower velocity at the end of the mixing process thanthe jet of entraining or driving fluid. The high velocity required forthe driving fluid for this purpose is achieved in that pressure energyis transformed into kinetic energy in a so-called injection nozzle ordriving nozzle. Finally, the remaining kinetic energy of the mixed jetis transformed into pressure energy again in a diffuser.

The driving fluid and driven fluid are chiefly gaseous media andvaporous media. The final velocity of a gaseous or vaporous drivingmedium is considerably greater than the speed of sound in jet pumps withhigh capacity and with a high pressure ratio. This is achieved by meansof a cross-sectional widening in the supersonic portion of the nozzle sothat potential energy is transformed into kinetic energy in conjunctionwith a simultaneous pressure drop. Supersonic nozzles generally have acircular cross section with a conical or contoured supersonic portion.

A steam jet pump in which the working steam is ejected from a jet nozzlewidening toward the end is described in German Patent publication3406201A 1 . The working steam achieves its critical velocity, i.e.,speed of sound, when passing through the neck portion of the nozzle.Since the steam passes through the widening portion of the nozzle, thepressure energy is completely transformed into kinetic energy and thesteam is ejected into a chamber at supersonic speed.

With the great differences in velocity between the load mass flow andthe driving mass flow, the mixing process in high-capacity jet pumps isinefficient and slow using this known jet pump design. This results inlosses in the process, particularly friction losses, and an excessivelylarge construction length of the jet pump or incomplete mixing andaccordingly output losses. It is not possible to manipulate thesupersonic flow in the supersonic core jet as is possible, for example,in the subsonic region, e.g., by means of interference bodies initiatingturbulence, in view of the considerable losses due to compressionshocks.

The usual increase in the mixing area between the driving or primary jetand the secondary jet effected in jet engineering by means ofrosette-shaped nozzles, known as hypermixing, is possible only in thesubsonic region. In the hypersonic region, such a step would immediatelylead to destruction of the jet momentum due to compression shocksresulting in failure of the pump.

THE SUMMARY OF THE INVENTION

The object of the present invention is to provide a jet pump and processfor operating the jet pump in which an increase in the mixing of drivingmedium and load medium is achieved in a simple design.

This object is met by the present inventive process for operating a jetpump with a driving nozzle from which a driving medium, especiallysteam, exits at supersonic speed and mixes with a gaseous load medium.Downstream of an outlet of the nozzle in the mixing region thecircumferential length is increased by a cross-sectional shape of thedriving jet deviating from the circle in order to eliminate azimuthalsymmetry of a vortex structure of the driving medium, so that therespective cross-sectional surface, in accordance with the principles ofcontinuity, begins in a jet direction with a circular cross section in asupersonic portion of the jet corresponding to the circularcross-sectional surface of the driving medium in conventional supersonicnozzles.

In addition, the object is met by a jet pump device, especially a steamjet pump, including a jet nozzle which widens from the neck to its endand which is enclosed by a coaxially arranged mixing chamber with aconically tapering diffuser portion adjoining the latter. Thecross-sectional shape of the widening portion of the jet nozzle is soformed by a neck of the transonic portion having a circular crosssection with corresponding circumferential length downstream of the jetthat the circumference has a greater length compared with the circularshape in a given cross-sectional surface and at least three beadsextending in the jet direction provided in the casing of the jet nozzle.

In conventional supersonic jets, vortex structures which move in thedirection of flow toroidally with azimuthal symmetry are generated atthe mixing boundaries downstream of the nozzle end cross section. Thisazimuthal symmetry is influenced according to the invention withoutdestroying the supersonic flow by generating vortex structures which areas large as possible and which lead to improved mixing and an expansionof the mixing zone. The interaction between these vortex structureshaving an axis of rotation in the direction of flow and toroidal eddiescommonly generated, that is, eddies with an azimuthal rotational axis,leads to pulsating, unsteady processes. The circumferential length ofthe respective cross-sectional shape is increased while retaining thecross-sectional surface in comparison with the respective circular crosssection and accordingly while retaining the mass throughput per secondand local status (pressure, temperature, Mach number). Proceeding fromthe circular cross section in the transonic portion of the drivingnozzle, corrugations or beads in the form of bulges or dents areprovided downstream in the supersonic portion at the outer surface ofthe nozzle. These corrugations or beads are rounded at their apex. Thecross-sectional surfaces can have the shape of a rounded triangle,square or polygon, e.g., hexagon. Downstream of these beads, arevortices, the rotational axes of which face in the direction of flow,which improve the mixing process in the difficult case of supersonicmixing. When using a steam jet pump with a fluid pressure or mediumpressure of 10 bar to 12 bar, the speed of the driving medium reaches4.8 to 5.2 times the speed of sound in such supersonic nozzles(hypersonic state).

In order to prevent thick boundary layers and compression nozzles, thecorrugation or bead-shaped bulges or dents are advantageously rounded attheir apex.

In the jet pump according to the invention, the pressure at the nozzleoutput exceeds the intake pressure of the load medium by a factor of 3to 5 and the end cross section is correspondingly reduced. Accordingly,the nozzle length can be shorter by a factor of 0.2 compared with thecalculated length with complete expansion to the intake pressure. As aresult of this step, the intensification of the mixture leads not onlyto a shorter mixer, but also to an improvement of the pressure ratio byapproximately 20%.

An advantageous construction is achieved in a gradually continuoustransition from the circular cross section to the end cross section ofthe supersonic driving nozzle. The change in cross section downstream inthe supersonic portion may correspond to the cross section of a conicalor contoured nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a jet pump in accordance with the present invention;

FIG. 2 shows the supersonic driving nozzle of the jet pump of FIG. 1;

FIG. 2 shows a cross-sectional view of the supersonic driving nozzle ofFIG. 2a along line III--III;

FIGS 4e through 4d show different cross-sectional shapes of the outletof the supersonic driving nozzle of FIG. 2a along line IV--IV;

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. I schematically shows the arrangement of a supersonic drivingnozzle 10 in a jet pump 20. The jet pump 20 has, arranged one after theother in series from a constructional view point, a cylindrical part 21,a sharply conical part 22 and a slightly conical part 23 of the mixeradjoined by a shock diffuser 24 and a subsonic diffuser 25.

Nozzle 10 has a length Xd and a calculated nozzle length Xr. The initialtemperature and initial pressure of a load medium are T0 and P0,respectively, and the final pressure at the output of the pump is P4.

FIG. 2 shows a schematic diagram of the supersonic driving nozzle 10.The neck 12 of the transonic region adjoins the entrance of the subsonicportion 11. A widened portion 13 of the supersonic region with theoutlet 14 and accordingly with the nozzle end cross section adjoins theneck 12.

Corrugations or beads 18 in the form of bulges 16 having a deformationangle β are provided in the upper portion of the supersonic drivingnozzle 10 in the casing 19 which has an angle γ . The deformation anglemeasured from an apex of the bulge 16 is greater than the casing angle γof a greater part of the jet nozzle casing 19 by 3° to 5°.

Corrugations or beads 18 in the form of dents 17 having bead angle areprovided in the lower region of the supersonic driving nozzle 10 in thecasing 19 having angle γ. The bead angle measured from an apex of thedent 17 is smaller than the casing angle δ of a greater part of the jetnozzle casing 19 by 3° to 5°.

FIG. 3 shows a cross section along line III--III having a circularcross-sectional surface Ak and a corresponding circumferential lengthLk.

FIGS. 4a through 4d show different cross-sectional shapes of thesupersonic driving nozzle in FIG. 2 along line IV--IV. Thecircumferential length Lk in a circular cross section of conventionalsupersonic nozzles is shown in dashes. In all examples, thecross-sectional surface A of the circular cross section in aconventional supersonic nozzle is equal to that of the nozzle providedwith carrugations or beads.

FIGS. 3a and 3b illustrate examples with three or four beads 18 in theform of bulges 16 in the upper region. Beads 18 in the form of dents 17in the lower region are illustrated in FIGS. 4c and 4d. As shown in FIG.4d, legs 15 open at an angle α of at least 60°.

What is claimed is:
 1. A process for operating a jet pump including adriving nozzle having a diverging supersonic portion with an outlet fromwhich a driving medium exits at supersonic speed and mixes with agaseous load medium in a mixing chamber coaxially enclosing the drivingnozzle and connected to a conically tapered diffuser, said processcomprising the steps of:increasing a circumferential length of a crosssection of the driving nozzle having a predetermined shape by changingthe shape of the cross section of the driving nozzle using corrugationsextending in a direction of jet flow in order to eliminate azimuthalsymmetry of a vortex structure of the driving medium in a mixing areadownstream of the nozzle, wherein beginning in the direction of jet flowa cross-sectional surface of the supersonic portion of the nozzle withthe corrugations is equal to a respective circular cross-sectionalsurface at the same cross-sectional locus.
 2. The process of claim 1,further comprising the step of generating in the cross section ofincreased circumferential length a vortex structure having an axis ofrotation in a direction of flow.
 3. A jet pump comprising:a jet nozzlehaving a neck and an outlet, said jet nozzle including a divergingcavity extending from the neck to the outlet thereby defining asupersonic portion therebetween; a mixing chamber coaxially enclosingsaid jet nozzle; and a conically tapering diffuser connected to saidmixing chamber, the neck having a circular cross sectional shape with afirst circumferential length; and means for increasing a circumferentiallength of a cross section of said nozzle, the neck having a circularcross sectional shape with a first circumferential length and downstreamtherefrom said nozzle casing having a portion with a non-circular crosssectional shape with a second circumferential length greater than thefirst circumferential length, and at least three deformations extendingin a direction of jet flow within the casing of said jet nozzle; whereinsaid nozzle has a length which is shorter than a calculated nozzlelength by a factor greater than 0.2 for complete expansion due to intakepressure of a load medium.
 4. A jet pump comprising:a jet nozzle havinga neck and an outlet, said jet nozzle including a diverging cavityextending from the neck to the outlet thereby defining a supersonicportion therebetween; a mixing chamber coaxially enclosing said jetnozzle; and a conically tapering diffuser connected to said mixingchamber, the neck having a circular cross sectional shape with a firstcircumferential length and downstream of the neck said jet nozzle casinghaving a portion with a non-circular cross sectional shape with a secondcircumferential length greater than the first circumferential length,and at least three deformations extending in a direction of jet flowwithin the casing of said jet nozzle; wherein said jet nozzle has alength which is shorter than a calculated nozzle length by a factorgreater than 0.2 for complete expansion due to intake pressure of a loadmedium.
 5. The jet pump of claim 4, wherein the jet nozzle casinggradually and continuously transitions from the circular cross sectionof the neck to an end cross section including the carrugations.
 6. Thejet pump of claim 5, wherein the carrugations are one of bulges anddents having a rounded apex and legs which are separated by an angle ofgreater than 60°.
 7. The jet pump of claim 6, wherein the deformation isa bulge and a corrugation angle measured from an apex of the bulge isgreater than a casing angle of a greater part of the jet nozzle casingby 3° to 5°.
 8. The jet pump of claim 6, wherein the carrugations is adent and a bead angle measured from an apex of the dent is smaller thana casing angle of a greater part of the jet nozzle casing by 3° to 5°.9. The jet pump of claim 4, wherein the jet pump is a steam jet pump.10. The jet pump of claim 4, wherein the supersonic portion of the ofthe jet nozzle with the corrugations has a cross-sectional surface equalto a respective circular cross-sectional surface at the samecross-sectional locus.